fix: Properly clean up RCTDevLoadingView on hide (#2201)

Author: Saadnajmi

packages/react-native/React/CoreModules/RCTDevLoadingView.mm

@@ -138,7 +138,7 @@ - (void)showMessage:(NSString *)message color:(RCTUIColor *)color backgroundColo
       self->_label.font = [UIFont monospacedDigitSystemFontOfSize:12.0 weight:UIFontWeightRegular];
       self->_label.textAlignment = NSTextAlignmentCenter;
 #else // [macOS
-      self->_window = [[NSWindow alloc] initWithContentRect:NSMakeRect(0, 0, 375, 20)
+      self->_window = [[NSPanel alloc] initWithContentRect:NSMakeRect(0, 0, 375, 20)
                                                  styleMask:NSWindowStyleMaskBorderless
                                                    backing:NSBackingStoreBuffered
                                                      defer:YES];
@@ -214,6 +214,8 @@ - (void)showMessage:(NSString *)message color:(RCTUIColor *)color backgroundColo
         }];
 #else // [macOS]
     [RCTKeyWindow() endSheet:self->_window];
+    self->_window = nil;
+    self->_hiding = false;
 #endif // macOS]
   });
 }